In the field of robotics and factory automation, high-speed, accurate multiple positioning of a workpiece is a common requirement. Hydraulics have been previously used but hydraulic systems are expensive and any leakage of hydraulic fluids produces a contamination problem which can not be tolerated in many applications including food packaging, biomedical assembly, electronics manufacturing or environments requiring clean-room conditions. In comparison to hydraulic systems, pneumatic systems are very cost-effective, are easily understood and maintained, and can be operated by a broad range of personnel. However, because air is compressible, pneumatic actuators alone are incapable of accurately positioning a workpiece in any more than the terminal positions, ie. their fully-extended and fully-retracted positions, at the end of each stroke. Currently there is a high demand for systems that are capable of accurately and repeatably positioning a workpiece at multiple locations. Typically, stepper motors or servo motors are combined with a ball-screw and linear actuator to produce such a positioning system. While these systems are quite accurate and produce repeatable results, they are very expensive and require a highly-skilled operator to integrate, setup, debug and run them. It is a general objective of this invention to provide a simpler, less costly but highly accurate positioning system.
A cost-effective, accurate and repeatable mid-stroke stopping and positioning method using pneumatics has not been successfully achieved by the prior art. Attempts have been made in the past, for example in U.S. Pat. Nos. 4,829,880 and 4,898,080, to locate a workpiece at any of several pre-set stop points but these attempts have not been successful. In the patented device a magnet is used to position a pivoted latching arm but this system has inherent weaknesses that have made it commercially unacceptable. First, pneumatic actuators have the ability to produce several hundred pounds of force. Therefore, the stopping mechanism must be robust enough to withstand these forces and still maintain accuracy and repeatability. In addition, once the worktable reaches a pre-set stop point, the pivoted latching arm used in the patented device becomes locked in place by the worktable. Therefore, the worktable must be backed off (moved in the reverse direction) to clear the latch, in order to allow forward motion to continue. Moreover, commercial products made under these patents did not have sufficient positioning accuracy or repeatability to meet the demanding requirements of the automation industry. In addition, there was no positive mechanical member holding the latch arm in an extended position.
In view of these and other shortcomings of the prior art, it is one object of the invention to provide a positive linear pneumatic positioning system capable of locating a worktable in one or any of a plurality of linearly arranged stop positions with an accuracy up to 0.001 inch to assure precision placement and assembly of parts held on the worktable.
Another object is to enable the workpiece to continue motion in a given direction after stopping without having to first back off in the reverse direction.
Still another object is to find a way of moving both the worktable and the stop arm using standard parts, namely, pneumatic actuators each consisting of a cylinder and a piston assembly that is commercially available.
A further object is to provide a positive linear positioning and stopping system that has the capability of advancing to the next pre-set position in a sequential manner or to advance to any of a plurality of pre-set positions in a random manner.
Another object is to provide both unidirectional as well as bi-directional positioning capabilities.
In addition, an object of the invention is to be easily adaptable to any of the various linear pneumatic actuator configurations that are commercially available today.
A further, more specific object is to provide a positive linear pneumatic positioning system that uses a first pneumatic cylinder and piston assembly for moving a worktable and a second pneumatic indexing cylinder and piston assembly for selecting a stop member that is to be placed in an operating position.
Another object is to provide a positive mechanical element for locking a selected stop member in an extended operating position.
These and other more detailed and specific objects of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.